In current building construction practice it is usual to install prehung doors, which is the industry expression for door assemblies that are delivered to the building site as a single unit including a door, the door jamb, and stop, with the door factoryaffixed on its hinges. However such door assemblies still have to be installed level and this has presented a problem of a place to attach the level while leaving the carpenter's hands free for the work of installation. Prehung doors are supplied left- or right-swinging, as required and they are highly standardized to a 13/8 inch (34.925 mm) door thickness for inside doors and a 13/4 inch (44.5 mm) door thickness for outside doors. There is a standard spacing between the door edge and the jamb and the door face and the stop that strictly limits the size of any objects that will be fit into these spaces during installation.
In a professional patentability search for the PTO files patents U.S. Pat. Nos. 991,446; 1,612,843; 2,171,616; 2,531,563; 2,915,273; 2,624,118; 3,123,918; 3,159,924; 3,826,013; and 4,501,057 were developed of which the following four seem to have the most relevance to the present invention:
Feldheim U.S. Pat. No. 2,531,563 describes a level holder which can be clamped to a table top or the top of a side wall but would be useless for attaching to the edge of a closed door since the level structure itself would come between the door and the jamb.
Anderson U.S. Pat. No. 2,624,118 describes a device for levelling the vertical edge of wallpaper, This also could not fit against the edge of a closed door and would be useless for my purpose.
Leiblein U.S. Pat. No. 3,159,924 has a level to attach to the side rail of a ladder. Leiblein's level indicator is positioned in a parallel plane to the rail (ladder edge) and could not be used for levelling my door.
Palomera U.S. Pat. No. 4,501,057 shows a level holder which, if used for my purpose would require the edge of the door to be brought up against the short width of his leg 24 with no extended contact against the plane to be measured. Neither would it provide any means for gripping my door.